The use of compositions that spontaneously combust or autoignite for a variety of purposes are well known. U.S. Pat. No. 5,421,835 to Harding discloses a new and improved fire starter composition which includes a liquid fuel component and a solid oxidant component retained in separation from the liquid fuel component until ready for use. The liquid fuel component is selected from the group consisting of glycerin, ethyl alcohol, isopropyl alcohol, and methanol, and mixtures thereof. The solid oxidant component is selected from the group consisting of potassium permanganate and potassium dichromate. To start a fire, a quantity of the fuel is added to a quantity of the oxidant. One object of the invention of the Harding patent is to provide a fire starter composition which takes the place of a match or other pyrotechnic material.
U.S. Pat. No. 3,754,511 to Damon et al. discloses a similar composition for a spontaneous chemical reaction, e.g. a hypergolic composition, for igniting a briquet of compressed mixed powered oxidants and reductants in a fuel unit. In particular, Damon et al. discloses, as a substitute for an electric squib, spontaneous chemical reactions such as that of glycerin and powdered potassium permanganate.
The concept of autoignition is also utilized in inflators, particularly those for air bag inflation in vehicles. Autoignition devices are typically employed in inflators so that the inflator does not malfunction or fail at elevated temperatures. The autoignition devices generally autoignite at temperatures well below those that would cause the inflator structural assembly to fail. In addition, the autoignition devices in inflators are designed to activate the inflator when a disposed automobile is to be burned out. In this way, no active chemical agents remain in the automobile. The autoignition devices are also designed to ignite when the inflator performs in its intended function.
U.S. Pat. No. 5,186,491 to Yoshida et al. shows a typical gas generation device for a vehicular passenger protecting system which includes an autoignition device. In this patent, a smokeless powder having a four-second ignition temperature of 175.degree. C. is used as the autoignition composition.
U.S. Pat. No. 4,561,675 to Adams et al. discloses another autoignition device. In this patent, the autoignition material is preferably a granular mixture of 25% by weight of boron and 75% of potassium nitrate plus or minus 10% of lead azide. The autoignition composition may also be any granule, powder other material which is stable for a long duration at temperature up to 121.degree. C. and will autoignite at a desired temperature of approximately 177.degree. C.
The autoignition devices of the prior art are not without their drawbacks. For example, autoignition compositions based on smokeless powder decompose when maintained at elevated temperatures for a long period and lose their effectiveness. Also, the use of lead compounds in autoignition compositions is generally avoided because of toxicity. Other problems may exist in inflator designs wherein the autoignition composition of the autoignition device may adversely affect the other ignitable compositions in the inflator device itself.
As such, a need has developed to provide improved autoignition devices or systems which overcome the drawbacks in the prior art.
The present invention responds to this need by using an autoignition composition which has its components divided by a separator with the melting point of the separator linked to the desired autoignition temperature of the system.